During the process of cleaning diesel exhaust,the Mn-based mullite SmMn2O5 is proved to display great potential as a replacement catalyst of Pt in NO oxidation.Fundamentally,there is rare study on the NO oxidation catalytic mechanism and the mullite physical properties.In this paper,the pure SmMn2O5 mullite nanoparticles have been synthesized.Furthermore,the optical measurements and the density functional theory (DFT) calculations have been performed to investigate the physical properties behind.